Treated grinding rods



Feb. 23, 1965 A. l. BARD ETAL, 3,170,64

Y TREATED GRINDING Roos Filed Oct. 16, 1961 2 Sheets-Sheet 1 l 1 'Il ATTORNEYS Feb. 23, 1965 A. l.. BARD ETAI. 3,170,641

TREATED GRINDING RODS Filed Oct. 16, 1961 2 Sheets-Sheryll 2 IN VEN TOR. ALBERT L. BARI: AND

B WAYNE B Ween,

Arronugvs.

United States Patent O 3,170,641 TREATED GRINDING RODS Albert L. Bard and Wayne B. Weed, Independence, Mo., assignors to Armco .Steel Corporation, .Middletowm Ohio, a corporation of Ohio Filed Oct. 16, 1961, Ser. No. 145,251 2 Claims. I(Cl. Z41- -1S4) This invention-relates to heat treated grinding rods. Such grinding rods are used in rod mills which in recent years have become increasingly importantes a comminuting deviceclassitied generally between fine crushing and coarse grinding. Thus, a rod mill has application as a line Crusher or as a coarse grinder. v'lfhe'output of a rod mill is then generally further commi-tinted as necessary in a ball mill which is classified as a fine grinder.

In connection withball mills, the grinding blallshave for many years been heat treated to harden them. Attempts have also been made to heat treat and harden grinding rods. The hardening of grinding rods, however,

is beset by problems not encountered in connection with f hardening grinding balls and therefore prior attempts to harden grinding rods have either been entirely unsuccessful or have produced a relatively low hardness.

The principal problem encountered is ythat if a grindingrod is subjected to a quenching treatment after heating in a furnace, the rod tends to warp or bend. So long as the hardness does not exceed about 325 Brinell as taken With a 10 mm. Hultgren Ball (35 on the Rockwell C Scale), such a rod can be machine straightened. If attempts are made to harden :to ahigher hardness, such as for example 600 Brinell (60 on the Rockwell C Scale), it becomes impossible to maintain the hardness and straighten the rod. Either the rod will break or the rod must be materially softened in order to be straightened.

In the trade, Vthe phrase commercial straightness means a deviation from the center line not greater than ione-quarter inch per live'feet of length. The term machine straight means a maximum lateral deviation of one-eighth inch in five feet. Any attempt to heat land quencha rod byv previous methods will result in a distortion much'more than commercial straightness and, 'if a desired hardness is achieved, such a rod cannot be straightened. I t must b el borne in mind that rods `commonlyused in rod mills may vary from a :diameter of three inches to four inches andhave a length from ten to sixteen feet. They may-weigh from about 240 pounds to about 700 pounds each. y

vWith the foregoing considerations in mind, it is an object of the present invention to provide a highcarbon abrasion resistant quenched and tempered steel rod having a surface hardness of at least 50 on the Rockwell C Scale, which rod is within the specifications for machine straight rod.

This and other objects of the invention which will be pointed out in greater detail hereinafter or which will be apparent to one skilled in the art upon reading these specifications, are accomplished by that certain construction and arrangement of parts and by that series of method steps of which the following are exemplary ernbodiments.

Reference is made to the drawings forming a part hereof and in which:

FIGURE 1 is a fragmentary elevational view of an apparatus for quenching the rods after they have been Vheated in a furnace.

the left end of FIGURE 1.

FIGURE 3v is a fragmentary plan view showing the s l 3,l7@,6ii Patented lFeb. 23, 1965 ice;

taining straight the grinding rods during the quenching operation. FIGURE 4 is a somewhat diagrammatic view on a smaller scale similar to FIGURE 3, showing the relation of the feeding and rotating apparatus to the heating furnace.

FIGURE 5 is a fragmentary perspective view of the quenching rings and associated apparatus;fand

FIGURE 6 is a cross-sectional View taken onA the line 6 6 of FIGURE on an enlarged scale. i

The grinding rods of this invention are usually made of high carbon steel (.60 to k1.0% carbon) although'fit is within the scope of the invention to modify the analysis in known ways if, for example, it is necessary to increase the hardenability of the steel. Briey, in the practice of the invention the rods are heated in a continuous furnace through which they are passed axially while being rotated, the speed of the rod through the furnace being such as to achieve in the rod a temperature of from about 1450 F. to about 1600 F. in order to austenitize the steel. It will of course be understood that any other means of heating such as rolling the lrods across the hearth of a sloping type furnace could be used, so long as they produce a uniformly heated rod. f K

As the rod emerges from the furnace in the ausztenitic condition, it enters the quenching 'apparatus in which it passes through a series of annular nozzles through which a suitable quenching medium is caused to impingeupon (the surface of the rod. As the rod' pass-es through the quenching rings, itis caused to rotate about its axis and it is mechanically constrained to remain in` straight condition.

The details of thev temperature to which :the rod is raised, the depth in from the surface to which the desired temperature penetrates, thetemperature and character of the quenching medium, and the speed through the quenching apparatus do notV constitute a part of .the present invention and the details of the `hea-t treatment are well known to those skilled in the art. By way of an example, however, a three-inch4 diameter bar wasl caused to move through the apparatus at a Alineal speed of about twelve feet per minute and in the particular apparatus this meant that each element of the rod was subjected to a period of about eighty seconds in the quench., Such rods had a surface hardness in excess of SGRC. If a higher orlower hardness is desired, the heat treatment "and quench may be modified iasis well known to those skilled inthe art. K Similarly, it will berunderstood that in'a grinding rod as inalgrinding ball it -is desirable that the core be softer thanrthe outer shell. It is desirable in a grinding rod having a surface hardness of 5() or above on the Rockwell C Scale, that the core have a hardness of at least 35 on the Rockwell C Scale. The details of temperatures and times necessary to achieve these conditions are well known to those skilled in the art and will not be described further.

The particular material of which the rods were made was a high carbon (not less than .60 carbon) alloy steel in hot rolled machine straightened condition. By the present method and with the use of the present apparatus, grinding rods have been produced with the surface hardness of 60Rc and with such rods the weight loss after 720v hours in the millV was 33.8% as against a Weight loss after 720 hours of 47.1% with conventional grinding rods.

Referring now to the drawings, and particularly FIG- URE 4, the furnace is shown diagrammatically atv 10 and v the rod being treated is shown at 11. As the rod emerges arrangement of rollers for feeding and rotating and mainfrom the furnace, it enters the quenching apparatus which 'comprises'a series of pairsv of interdigitated skewed rollers 12, 13, etc. In FIGURE`4, only the first two pairs are Vshown in FIGURES 3 and'4, they form'what may be termeda two point support for the grinding Arod 11 Las best seen in'FIGURl-IZ.` All of the rolls of these pairs are driven inthe same ldirection of rotation whereby the rod arrows 31.' in VFIGRE 6. Preferablyfthe direction' of 11 supported thereon is caused to rotate about its axis.

Because the pairs of rolls are skewedasclearly seen in FIGURES `Zand 3, they cause the rrodto be fed axially in thegdirection of the arrow (FIG. 4) while it is being rotated. j

In order to enforce upon thefrod a straight condition during its passage throughr'the quenching apparatus, `there the conical annular sheetof quenching medium'is such that it'impinges against the surface of the rod 11 in the same vdirection "as the direction yof rodtravel, except for the last Vquenching ring,\which is reversed to stop the water fromfollowing the i-rod. Y

It will thus beclear that as the rod passes through the apparatus moving'axially and rotated about its axis, it is subjected to a plurality of annular sheets of water or other quenching medium. Y

The various pairs of. rollersA 1.2,4 13, etc; may be driven from a suitablek prime mover Ior prime movers (not shown) by means of a sprocket chain korithe like 40 engaging the sprockets 41 and 42. These sprockets,v as shown, respectively driverthe'rollers `of the first pair-12 through the lconnecting rods43, 44, each of whichis provided with is associated with each pair of rolls-12, 13, etc. a third roll 12a, 13a, etc., and this roll is mounted to ride on top of` the rod 11 and it is strongly pressed against the rod lby meansv of springs 12b, 13b, etc. which urgerthe respective roll mounting member 17 downwardly. The rollers 12a, 13a., etc. are mounted on the members '17. v The reason for the spring mounting .is to permit use of the apparatus with grinding rods of different diameters but it Lwill be seen that the springs will exert a Astrong force to press they respective-rolls 12m-13a, etc. against-the rods 11 as it passes through the apparatus. VIfnecessary Vto insure a straight condition, this third roll may use a positive positioning means such as-a screw` in place ofthe spring. v ,Y

Between the various pairs' of rollers *described above.,

there are disposed the quench rings 20. In the. particular embodiment illustrated therer are ktwo quench rrings 20 between each set of rollers.

The quench rings 26 are disposed so that the rod being i are kconnectedto a header 25. Thesefheaders are connected, as best seenin FIGURES l and 2, to a. suitable pump diagrammatically illustratedY asbeing within .the

The` connections-.21 to the various quench boxld in FIGURES 1 and 2. Thus, each of thequench TheY quenchvring itself, as

` V'rings `20 is supplied with quenching medium'attw'o dia- Y m'etricallyy opposite points.

' best seen in FIGURE 6and which may be madein two *50 pieces `27, 28 providedwith suitable sealing means vas at.

f 29v and bolted together, provides an annular space 30 connectingwith the'connections .21 and 22 `so that .the ring providesanannular conical nozzlethrough-which a generally conical sheet'of water emerges as indicated by theA a universal joint connection vat each end; The second pair of skewed rollers 113 is then'driven'fr'om the V.first pair 12 through .the connecting rods 45, 46, ywhich again arev provided withfuniversal jointsat .each end, as clearly shownv in 'FIGURE '3. y

It will be clear that various modifications may be made without departing lfrom the spirit of the invention VYand no limitations not specifically -sehforth `in they claims are intended. j

`.llheinvention having now been fullydescribed, what is lclaimediand. what it lis ,desired to secure `by Letters Patentis:

l. A high carbon,y abrasionresistant steel rod for rod mills, having avsurface hardness in excess of` on the Rockwell C Scale, said rod being straightwithin 1/8 inch inve lineal'feetoflength Y Y .Y 2. Aehigh .carbon,vabrasion resistantv steel rod for rod Y VVmills, having asurface hardness'in excess of 50 on the Rockwell C Scalegand a .core hardness 'of at least 35 on the RockwellCfScale'the hardness varying .gradually from.

the surface to the'center of said'rod, said rod'being straight within 1/8 inch'inve lineal Afeet ofi length,

' v References einen kin theme f kthis patent UNITED STATES-PATENTS 1 v VOTHER REFERENCES. n

NACO Grinding fBalls, vMining Engineering, July .1959, page 7,32. t n 

1. A HIGH CARBON, ABRASION RESISTANT STEEL ROD FOR ROD MILLS, HAVING A SURFACE HARDNESS IN EXCESS OF 50 ON THE ROCKWELL C SCALE, SAID ROD BEING STRAIGHT WITHING 1/8 INCH IN FIVE LINEAL FEET OF LENGTH. 